The present invention relates to network interfacing, and more particularly, to methods and systems for controlling transmission of data between network stations connected to a telephone line medium.
Local area networks use a network cable or other media to link stations on the network. Each local area network architecture uses a media access control (MAC) enabling network interface cards at each station to share access to the media.
Conventional local area network architectures use media access controllers operating according to half-duplex or full duplex Ethernet (ANSI/IEEE standard 802.3) Protocol using a prescribed network medium, such as 10 BASE-T. Newer operating systems require that a network station to be able to detect the presence of the network. In an Ethernet 10 BASE-T environment, the network is detected by the transmission of a link pulse by the physical layer (PHY) transceiver. The periodic link pulse on the 10 BASE-T media is detected by a PHY receiver, which determines the presence of another network station transmitting on the network medium based as detection of the periodic link pulses. Hence, a PHY transceiver at Station A is able to detect the presence of Station B, without the transmission or reception of data packets, by the reception of link pulses on the 10 BASE-T medium from the PHY transmitter at Station B.
Efforts are underway to develop an architecture that enables computers to be linked together using conventional twisted pair telephone lines instead of established local area network media such as 10 BASE-T. Such an arrangement, referred to herein as a home: network environment, provides the advantage that existing telephone wiring in a home tray be used to implement a home network environment. However, telephone lines are inherently noisy due to spurious noise caused by electrical devices in the home for example dimmer switches, transformers of home appliances, etc. In addition, the twisted pair telephone litter suffer from turn-on transients due to on-hook and off-hook and noise pulses from the standard POTS telephones, and electrical systems such as heating and air conditioning systems, etc.
An additional problem in telephone wiring networks is that the signal condition (i.e., shape) of a transmitted waveform depends largely to the wiring topology. Numerous branch connections in the twisted pair telephone line medium, as well as the different associated lengths of the branch connections, may cause multiple signal reflections on a transmitted network signal. Telephone wiring topology may cause the network signal from one network station to have a peak-to-peak voltage on the order of 10 to 20 millivolts, whereas network signals from another network station may have a value on the order of one to two volts. Hence, the amplitude and shape of a received pulse may be so distorted that recovery of a transmit clock or transmit data from the received pulse becomes substantially difficult.
An additional problem encountered in European telephone systems involves the use of a network termination basic access (NTBA) device, used as an interface between the residential customer premises and a central office of the public switched telephone network for transmission of Integrated Services Digital Network (ISDN)-based signals. In particular, NTBA devices map a two-wire ISDN signal from a central office into a 4-wire S0 bus having a 2-wire send path and a 2-wire receive path for sending and receiving the ISDN-based signals throughout a customer premises. The ISDN-based signals generate harmonic reflections on the S0 bus that cause substantial interference with the higher-frequency network signals. Moreover, the zero crossing of as ISDN-based signal interferes substantially with the transmitted network signals rendering the transmitted network signal unusable due to the harsh conditions on the 4-wire S0 signal bus.
There is a need for an arrangement for interconnecting computer end stations in a home telephone network having a network termination basic access (NTBA) device and configured for sending ISDN-based signals on a 4-wire bus.
There is also a need for an arrangement for implementing a home computer network in ISND-bases customer premises configured for sending and receiving ISDN-based signals on a 4-wire S0 bus.
These and other needs are attained by the present invention, where a low pass filter is coupled to a 2-wire send path for attenuation of harmonics of ISDN-based signals that interface with transmitted network data signals. The low pass filter also delays the ISDN-based signals relative to the network data signals to minimize interference by the ISDN-based signal.
According to one aspect of the present invention, a method is provided of implementing a local area network is a hone telephone network having a network termination basic access (NTBA) device, configured for sending and receiving ISDN-based signals to and from a public switched telephonic network, and a four-wire bus including a two-wire send path and a two-wire receive path for sending and receiving the ISDN-based signals, respectively, between the NTBA device end taps along the four-wire bus. The method includes connecting a low pass filter, configured for passing the ISDN-based signals and rejecting harmonics thereof, between the two wires of the two-wire send path, and transmitting network data signals having frequencies substantially higher than the ISDN-based signals, between the taps.
According to another aspect of the present invention, a computer network includes a network termination basic access (NTBA) device, configured for sending and receiving ISDN-based signals to and from a public switched telephone network, a four-wire bus a two-wire send path and a two-wire receive path for sending and receiving the ISDN based signals between the NTBA device and ISDN customer premises equipment, first and second end stations configured for exchanging network data signals, having frequencies substantially higher than the ISDN-based signals, via at least one of the two-wire send path and the two-wire receive path, and a low pass filter. The low pass filter is coupled to the two-wise sand path for passing the ISDN-based signals and filtering harmonic signals of the ISDN-based signals substantially at the frequencies of the network data signals, the low pass filter enabling transmission of the network data signals via the at least one of the two-wire send path and the two-wire receive path.
Additional advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.